1. Field of the Invention
The present invention relates to a tuner block for a broadcasting signal receiving apparatus such as a VCR, and more particularly, to a tuner block having a modulator, a tuner and IF/demodulator circuit which are built integrally in a casing.
2. Description of the Related Art
As shown in FIG. 1, a broadcasting signal receiving apparatus such as a VCR comprises an A/V block 10 for processing a video signal and an audio signal, a deck 20 for recording/reproducing the video signal and the audio signal on/from a recording medium such as a magnetic tape, a tuner block 50 for demodulating the video signal and the audio signal from the broadcasting signal transmitted through an antenna 60, and a CPU 30 which controls the broadcasting signal receiving apparatus. The tuner block 50 has a tuner 53 for tuning the broadcasting signal, an IF/demodulator circuit 55 for demodulating the tuned broadcasting signal, and a modulator 51 for modulating the video signal and the audio signal into an RF signal for a TV 70.
Generally, the modulator 51, the tuner 53, and the IF/demodulator circuit 55 are integrally built in a casing, and such a device is called as an integral-type of tuner block. The tuner block 50 is mounted on a printed circuit board in the VCR. The tuner block 50 is connected with other devices such as the A/V block 10 and the CPU 30 mounted on the printed circuit board.
FIG. 2 is a view showing an appearance of the conventional tuner block 50 that has the modulator 51, the tuner 53 and the IF/demodulator circuit 55 integrally formed therein. FIG. 3 is a view showing a layout of an arrangement of a plurality of pins of the tuner block 50 shown in FIG. 2.
As shown in FIG. 2, the tuner block 50 has a casing 50c for embracing the modulator 51, the tuner 53, and the IF/demodulator circuit 55, and an antenna input terminal 50a and an antenna output terminal 50b disposed at an outside of the casing 50c. The antenna input terminal 50a is connected with the antenna 60, and the antenna output terminal 50b is connected with the TV 70. A length of the casing 50c is standardized as 85 mm considering the arrangement of the plurality of pins installed on the casing 50c. 
As shown in FIG. 3, twenty-two pins are installed in the casing 50c. The 22 pins consist of five pins (pin 1 through pin 5) corresponding to the modulator 51, twelve pins (pin 6 through pin 16 and pin 21) corresponding to the tuner 53, and five pins (pin 17 through pin 20 and pin 22) corresponding to the IF/demodulator circuit 55.
The five pins allocated to the modulator 51 comprise pin 1 and pin 5 (AUDIO IN, VIDEO IN) to input the audio signal and the video signal, respectively, pin 2 (CH/SW) to input a channel selection signal, pin 3 (MB (5V)) to supply electrical power needed for the modulator 51, and pin 4 (CONTROL) to input a control signal for a mode conversion between a TV mode and a VCR mode.
The twelve pins allocated to the tuner 53 comprise pin 6 (RF AGC) to control a gain of an input signal, pin 9 and pin 10 (SCL, SDA) connected with control buses to communicate with the CPU 30 through I2C communication, pin 13 (X-TAL IN) to input a clock signal, etc. Among the twelve pins allocated to the tuner 53, pin 7, pin 11, and pin 15 are not used.
The five pins allocated to the IF/demodulator circuit 55 comprise pin 19 and pin 22 (AUDIO OUT, VIDEO OUT) to output an audio signal and a video signal, respectively, pin 20 (SIF OUT) to output a sound sub-carrier, etc. Among these pins allocated to the IF/demodulator circuit 55, pin 17 and pin 18 are not used.
Such an arrangement of the pins is determined considering the position of three ICs (Integrated Circuits) corresponding to the modulator 51, the tuner 53, and the IF/demodulator circuit 55 disposed in the casing 50c. In other words, the ICs, which correspond to the modulator 51, the tuner 53, and IF/demodulator circuit 55, are consecutively disposed from an adjacent place to the antenna input terminal 50a and the antenna output terminal 50b in the casing 50c. Considering the position of the ICs, the pins used by the modulator 51 are disposed near to the antenna input terminal 50a and the antenna output terminal 50b, the pins used by the tuner 53 are disposed at a next position, and the pins used by the IF/demodulator circuit 55 are disposed at a farthest place from the antenna input terminal 50a and the antenna output terminal 50b. 
Moreover, the arrangement of the pins is determined considering a necessity of maintaining a distance between pins which conduct signals that may cause interference if the pins are disposed closely to each other. For example, where the video output pin and the audio output pin are closely disposed, the video output signal causes interference to the audio output signal, thus noise is added to the audio signal. Therefore, the video output pin and the audio output pin are disposed respectively at pin 22 and pin 19 so as to be spaced by more than a predetermined distance.
However, a size of the conventional tuner block 50 becomes unnecessarily large since more pins are disposed than the number of pins actually needed for the broadcasting signal receiving apparatus. In other words, as described above, pins 7, 11, 15, 17, and 18 are not necessary since these pins are not used. Yet, the conventional tuner block 50 has the pins that are not used, thus the size of the tuner block 50 becomes unnecessarily large. Thus, it is difficult to realize a compact broadcasting signal receiving apparatus because of the unnecessarily large tuner block 50.
Recently, an IC having an integrally formed tuner and IF/demodulator circuit has been developed. Therefore, a tuner block having simpler construction may be manufactured by installing two ICs (a modulator IC and the integrated tuner and IF/demodulator circuit IC) in the casing. Accordingly, a small-sized tuner block may be created.
However, the arrangement of the pins according to the position of the modulator IC and the integrated tuner and the IF/demodulator circuit IC in the casing 50c, and signal interference problem between the pins in accordance with the position of the pins should be considered, even in the case of manufacturing the tuner block by adopting the IC in which the tuner and the IF/demodulator circuit are integrally formed. Therefore, to move some of the used pins to the position of the unused pins (pin 7, 11, 15, 17, 18) to reduce the number of the pins complicates construction of a circuit that connects the modulator IC and the integrated tuner and IF/demodulator circuit IC in the casing 50c and increases a probability that noise caused by the signal interference will be generated.